Devin Moore was pulled from the pool as his 4-year-old sister was being revived, Gwinnett police Cpl. R.B. Rude said. While Devin's sister was in stable condition Sunday at Gwinnett Medical Center, the boy was pronounced dead at the hospital.

About 30 children were attending a private event at the pool Sunday night when a lifeguard spotted the girl under the water, Rude said. The girl was not breathing but was revived with CPR.

While the girl was being resuscitated, someone pulled Devin from the water, Rude said. Although CPR was performed on the boy as he transported to the hospital, he did not survive.

The Gwinnett County Fire Department was called to the pool at 7:52 p.m. Sunday, fire Lt. Thomas Rutledge said. The girl, whose name has not been released, was alert and breathing when firefighters arrived.

The pool ranged in depth from 1.6 to 3.6 feet, Rutledge said.

The children's mother was at the pool, and three lifeguards were working that evening. The lifeguards rotated shifts, working for 30 minutes before taking a 15-minute break, Rude said.

All lifeguards at county-operated pools are certified under the American Red Cross' Lifeguard Training Program. The program includes 36 hours of training in topics such as CPR professional rescuer training, first aid and water park features.

Private party rentals at the Bogan Park Aquatic Center can accommodate up to 194 people, according to a news release. Private parties are booked for two-hour blocks after the pool closes on Fridays, Saturdays and Sundays.

"The Gwinnett County Board of Commissioners regrets this tragic event," Gwinnett County Commission Chairman Charles Bannister said in a news release. "We extend our thoughts and prayers to those who are so deeply affected by this tragedy."